Added new exception RpcErrorException to allow you to return a specific code and error object back to the other side

Author: david-driscoll

src/JsonRpc/RequestRouterBase.cs

@@ -153,6 +153,11 @@ public virtual async Task<ErrorResponse> RouteRequest(TDescriptor descriptor, Re
                         _logger.LogDebug("Request {Id} was cancelled", id);
                         return new RequestCancelled();
                     }
+                    catch (RpcErrorException e)
+                    {
+                        _logger.LogCritical(Events.UnhandledRequest, e, "Failed to handle notification {Method}", request.Method);
+                        return new RpcError(id, new ErrorMessage(e.Code, e.Message, e.Error));
+                    }
                     catch (Exception e)
                     {
                         _logger.LogCritical(Events.UnhandledRequest, e, "Failed to handle notification {Method}", request.Method);

src/JsonRpc/RpcErrorException.cs

@@ -0,0 +1,22 @@
+using System;
+
+namespace OmniSharp.Extensions.JsonRpc
+{
+    public class RpcErrorException : Exception
+    {
+        public RpcErrorException(int code, object error)
+        {
+            Error = error;
+            Code = code;
+        }
+
+        public RpcErrorException(int code, object error, string message) : base(message)
+        {
+            Error = error;
+            Code = code;
+        }
+
+        public object Error { get; }
+        public int Code { get; }
+    }
+}